Calculate Proportion of a Group

Question

I am trying to compute the fraction (%) of a each record from the group total in a dataframe. My data look like:

Where I have factors for Station, Month and PH

Answer 1

You can do it without summarise and it will work as expected. I doubled your data example so I have 2 groups to work with to show how it works.

library(dplyr)

bn_phyla %>% 
  group_by(Station, Month) %>% 
  mutate(prop = SumOfTotal_Caught/sum(SumOfTotal_Caught))

# A tibble: 8 x 5
# Groups:   Station, Month [2]
  Station Month  Phylum     SumOfTotal_Caught  prop
  <chr>   <chr>  <chr>                  <dbl> <dbl>
1 A       Feb-18 Annelida                  20 0.182
2 A       Feb-18 Arthropoda                20 0.182
3 A       Feb-18 Mollusca                  30 0.273
4 A       Feb-18 Nemertea                  40 0.364
5 B       Mar-18 Annelida                  40 0.333
6 B       Mar-18 Arthropoda                30 0.25 
7 B       Mar-18 Mollusca                  30 0.25 
8 B       Mar-18 Nemertea                  20 0.167

data:

# data_frame comes from dplyr
bn_phyla <- data_frame(Station = c(rep("A", 4), rep("B", 4)),
                       Month = c(rep("Feb-18", 4), rep("Mar-18", 4)),
                       Phylum = c("Annelida", "Arthropoda", "Mollusca", "Nemertea", "Annelida", "Arthropoda", "Mollusca", "Nemertea"),
                       SumOfTotal_Caught = c(20,20,30,40, 40,30,30,20))